1 Corinthians 3:18 (KJV 1900)
18 Let no man deceive himself. If any man among you seemeth to be wise in this world, let him become a fool, that he may be wise.
Paul is addressing the man in verse 17, who would defile the temple of God. Let that man not deceive himself. Paul used the word deceive in other passages. Paul was deceived by the law once (Romans 7:11), and it killed him spiritually. In Romans 16:18, he says those who do not adhere to sound doctrine deceive the hearts of the simple in the church.
Therefore, men should not be deceived by their worldly wisdom. If there is any man in the church who looks on himself and his sophisticated knowledge with pride, he needs to knock himself down a notch. Let him become a fool, in other words, know Jesus Christ, and him crucified (2:2). Then that man will be wise.